Cable??

[Adam F]

Right....went down to towsure and bought a battery yesterday. Bargin - 85ah, 28 quid!

 

Now I need some cable to wire it in. I have changed my original plans as I dont have alot of room under the transom, so the batt is going in the console locker. Good as it puts weight up the front and is out of the way, but bad as it is 5.5m from the other batt and the isolation switch!!!

 

I need 5.5m of + and 5.5m of - cable.

 

Where from??????? Also the clamps and crimps?????? Also do I need to fuse this? I have fuses after the batt and before the engine and switch panel, do I need another??????

[Newboy]

Again these people are very competitively price

 

http://www.vehicle-wiring-products.co.uk/V...epage/home.html

 

they have everything you'll need.

 

Alternatively, see if you have any old jumping cables lying around redundent, they make fine battery cables too.

[Afishionado]

Right....went down to towsure and bought a battery yesterday. Bargin - 85ah, 28 quid!

 

Now I need some cable to wire it in. I have changed my original plans as I dont have alot of room under the transom, so the batt is going in the console locker. Good as it puts weight up the front and is out of the way, but bad as it is 5.5m from the other batt and the isolation switch!!!

 

I need 5.5m of + and 5.5m of - cable.

 

Where from??????? Also the clamps and crimps?????? Also do I need to fuse this? I have fuses after the batt and before the engine and switch panel, do I need another??????

In a nut shell ......DON'T DO IT!

I don't know the formula but experiance tells me that there would be an unreasonable electrical resistance with that length of cable and the voltage drop could reduce your starting ability. Not only that at starting volts/amps demand there could be a risk of heat build up if too thin a wire was used. Something quite substantial like quality jump lead wire would be required.

Best practice is to have the battery as near to the power demand as possible.

 

Mike

[Newboy]

Also the heavy plates dictate that battery must have minimum of movement, therefore the stern is the best place.

[Paul D]

Adam,

 

Mike is quite correct. 5.5 metres of cable run will cause way too much voltage drop when starting the engine ( You will get away with running instruments etc. but definitely not starting the engine, which is the main reason you want a second battery IMHO ).

 

Of interest, even on my boat I was getting too much voltage drop when transmitting on the radio at high power ( when switched to battery 1 ), need to check the wiring me thinks!!, but there again I can start the engine on both with no trouble

 

 

Say starting the engine takes around 100 Amps surge ( which is even possibly a low estimate ) and your cable is 2 mm diameter ( AWG 12 - my guess ) , this will have a resistance = .00547 * 5.5 metres Ohms = 0.03 Ohms.

 

The voltage drop = current times resistance ( V=IR ) = 0.03 * 100 = 3 VOLTS.

 

Therefore your 12 volts will become 9 volts when cranking the engine...

 

If the cable were only 1 metre long then the voltage drop will be around 0.5 VOLTS which is much more manageable.

 

Also the cable will warm up if you keep cranking as you will be using 300 Watts of battery energy to warm up the cable ( 3 Volts * 100 Amp )

 

 

[Afishionado]

I knew Paul D would have the math's .

 

I just glad that someone scientific could put numbers to my 'seatof the pants' knowledge

 

Mike

[Adam F]

Bugger!

[domino]

Adam,

 

I have exactly the set-up you propose - Factory fitted marine battery at rear with switch and second battery in steering console - it has been operating perfectly satisfactorily for 3 years.

 

I agree 2mm dia wire is no use, but why would you consider using wire thinner than the existing cables from battery to starter??

 

My second battery is connected to the switch/batt 1 with 10sqmm cables... basically the same size as the existing cables from the engine to the original battery.

 

All lights and electronics are connected to Batt 2... which is a standard 60Ah car* battery.

 

*I don't agree with using a leisure battery... if the main battery fails I would rather be able to start the engine with the back-up, than have it there just to make sure the radio works so that I can call the coastguard!

 

I normally start the day with the switch set to Batt 1... at some point during the day I will changeover to Batt 2, to top the charge. The engine starts fine on Batt 2... on occasions I have forgotten to siwtch back to Batt 1 at the end of the day - next trip the cold engine fires up staight away on Batt 2... no problem.

 

I never use the BOTH position on the switch... if one battery fails, it will very quickly drag down the other one.

 

As stated in the earlier thread... NEVER swicth between batteries through the OFF position with the engine running.

 

My boat lives at the boatyard so I don't have the option to keep batteries charged up at home... with this set-up, I don't need to. I don't get to use the boat much through the winter, so I take the batteries home at the end of the season and keep them in the garage, where they get a couple of top charges before going back in the boat in the spring.

 

Just my two-penny worth... but it works for me.

[Adam F]

Now Im really confused!!!! The console battery is my prefered choice, and Whippet says this is fine, however I am concerned about loosing power over the 5.5m run......

hhmmmmmmmmm

[domino]

Adam,

 

Have a look at http://www.tooled-up.com/Product.asp?PID=26689.

 

These 5m jump leads are rated at 600A, using 25sqmm cable.

 

If you want to be on the safe side then just use thicker cable... I used 10sqmm because it was readily available from work.

 

Step up to 16sqmm or even 25sqmm, as with the jump leads, and I don't think you will have any problems.

 

I've been trying to find some typical resistance figures for 10sqmm cable, but so far been unlucky... bloody useless internet!

 

Alan

[Adam F]

So do you think that I will suffer from resistance and / or heat build up using 10 / 16 sqmm cable?

[Bob F]

Paul,

 

I agree with you figures if using 2mm copper wire, but typically you would use 10mm or 16mm cable for battery connections.

 

For 2mm copper cable the standard resistance per meter is 0.005488 ohms.

 

For 10mm copper cable the resistance per meter will be 0.0002195 ohms. (by my calculation)

 

For 16mm copper cable the resistance per meter will be 0.0000857 ohms.

 

(resistance is inversly proportional to the square of the diameter). In other words, the thicker the wire the less the resistance.

 

So, for 5.5m of 10mm cable the resistance will be 0.0002195 x 5.5m = 0.0012 ohms.

 

Which gives a voltage drop of 0.0012 x100A = 0.12 volts (for 10mm cable)

 

 

For 5.5m of 16mm cable the resistance will be 0.0000857 x 5.5m = 0.00047 ohms.

 

Which gives a voltage drop of 0.00047 x100A = 0.05 volts (for 16mm cable).

 

 

By my calculations, it shouldn't be a problem fitting the battery in the console, if you are using suitably sized cables, so I have to agree with Whippet. Just make sure all the connections are tight.

 

Also, a Marine Battery is designed to be able to start motors as well as running your instruments. A Leisure Battery is designed primarily for running your instruments, and not for repeated starting of a motor. So, if you fit a Leisure Battery as you second battery, try to only use it for occasional starting of your motor. It will start the motor, but you will eventually damage it if you keep trying to start a motor that is relunctant to fire, for example.

 

But with all the "senior moments" I've been having recently, it might be an idea to check my calculations.

 

[Newboy]

use a set of jumplead as temp cables, if it works without overheating, then get some thick cables and make it permenent.

 

Or give the vehicle wiring place a ring and ask 'What's the max length cable I can use for bridging two batteries?' They are bound to know.

[duncan]

at the risk of looking really daft how about -

 

1. Wire the new battery where you wish

2. Use cable appropriate to the charging side and demand side excluding starting!

Do not wire it so that it can be called upon by the starter solenoid.

If your new battery has the same terminals as the old then if you get a battery failure on your starter motor you can quickly swap and get home. If not add a basic set of jump leads to your boat kit and jump the two batteries if you get a starter battery failure. Note you are less likely to get a flat starter battery when out for a long summer trip as the leisure one will be running the lights, electronics, radio, baitwell, fridge, dvd player, aircon........

[Paul D]

Bob,

 

Why I calculated for 2 mm I am unsure ( seems I am having senior moments too !!).

I agree with your calcs for 10 mm cable ( and 16 mm cable ).

 

Got me thinking too now as well, since I could do with shifting some weight in my boat forward ( saves telling Mike to sit at the front

 

 

So Adam I think you will be fine provided you use some heavier cable ( all that weight of copper eh ).

 

 

 

 

[Coddy]

Hi Adam

 

My 165 has the engine start battery in the console and my back up inside the cuddy behind the console on the seat area.

 

Not pritty but it works fine and was installed by Warrior!

 

I just don't have a change over switch and only use back up battery for everything except starting.

 

As Duncan suggests, if I get a flat battery I just have to swap terminals over from one battery to the other ........ no problem

 

May be a bit differant in a rolling sea

 

Coddy

[domino]

Hi Adam

 

......... May be a bit differant in a rolling sea 

 

Coddy

... and in a blind panic, being blown towards the rocks, searching for the correct size spanner!!!

 

My advice... fit a switch.

[duncan]

valid point whippet but I don't think batteries fail just like that, especially if you have a leisure one handling the onboard drain.

 

also, and I am sure your point was exagerated, if you are drifting close to rocks you wouldn't switch off your engine and, if anchored you wouldn't haul anchor before starting engine.

[Newboy]

Myself has opted for the 'unplug and plug' method, I've fitted my engine battery with 'quick release' terminals, equipment battery is via 2 spring clips, so they can all be disconnect and connect in a flash. I also carry one of those power station capable of jump starting a battery in case both the batteries failed.

 

My cabin is a maze of wires with lights, ff, gps, vhf as it is .....

[Maverick Martin]

Adam

 

If I was to retrofit two bats I would use a switch as suggested by whippet. You never know when you are going to need that extra bat. Sods law says it will more likely be when one or two other things are happening. Much easier to turn a switch.

 

Duncan has pointed out some instances when it wouldnt be urgent but what if your anchor is dragging or that gin palace which is on auto pilot without a body at the helm is bearing down on you or your engine conks out at a critical time. You would need all the power you could get and in double quick time.

 

Martin

[Paul D]

and the switch costs only around

[duncan]

I don't disagree that being able to start the engine from either battery is 'better'.

 

Will be a little more than a switch to achieve this - about 12 metre of battery cable for starters! Small price for safety though.

 

On safety I do hope all you outboard owners carry a spare starter circuit fuse...?

[domino]

I think you'll find Adam's boat has the switch fitted already.

 

I was pointing my advice at anyone else who is yet to fit a second battery and those with seperately wired batteries.

 

As I said before... it's the way I prefer it... and it works for me , if others are happy with other set-ups... well that's fine also.

[Adam F]

On safety I do hope all you outboard owners carry a spare starter circuit fuse...?

 

.....is that just a normal glass tube fuse????

[Adam F]

Right!....all done! - Took me most of the day though

 

I have my 85ah battery in the steering console. I have fitted a strap and 2 fairing blocks to stop the battery moving or sliding either left to right, forward or back or up and down.

 

I went to Guardian Autoelectrics on the Woolsbridge Ind. Est on the reccommendation of a mechanic friend.